ENTOMOLOGY IN OUTLINE — HEMIPTERA. 53 



These females give birth to new broods, all of which are still females, 

 and only females are born. This peculiar propagation is continued 

 throughout the summer. In the autuuni, however, when the weather 

 grows colder, the last births are both male and female, and these last 

 born females only lay eggs, which remain dormant until the following 

 spring, when they hatch out females, and the same process continues 

 without end. 



Some naturalists bold that if the conditions are right the aphis will 

 continue to give birth to females indefinitely without the presence of 

 males. Kyber records having had a rose aphis which produced young 

 for four years, and from his careful experiments it has been asserted 

 that under certain circumstances a female aphis may, in the entire 

 absence of males, continue propagating to infinity, providing that the 

 necessar}^ conditions — food and heat — for the development of the young 

 are not wanting. 



The color of the eggs of the aphis, together with their rarity, makes 

 them difficult to discover. During the months of February and March, 

 when the leaf buds of the rose begin to swell, the eggs of the rose aphis 

 may be seen like grains of gunpowder fixed within the crevices of the 

 bark. A single insect hatched from one of those shining black eggs 

 may be the progenitor of many billions of young during her lifetime. 

 Latrielle, who is an authority on this branch of entomology, makes a 

 curious calculation. He says that one female will produce young at the 

 rate of about twenty-five a day during the summer months, and one aphis 

 may be the mother of the enormous number of 5,904,000,000 during 

 the month or six weeks of her existence. Tongard and Morren, equally 

 good authorities, extend this number into quintillions, as being within 

 the capabilities of a single mother's efforts. Professor Huxley makes a 

 calculation which affords an approximate idea of what a quintillion of 

 aphids might mean. Assuming that an aphis weighs as little as the 

 one-thousandth part of a grain, and that it requires a man to be very 

 stout to weigh more than two million grains, he shows that the tenth 

 brood of aphids alone, without adding the products of all the genera- 

 tions which precede the tenth, if all the members survive the perils to 

 which they are exposed, contains more ponderable substance than five 

 hundred million stout men; that is, more than the whole population of 

 China and the United States combined. Fortunately there are large 

 numbers of carnivorous insects which prey upon the aphids and pre- 

 vent their inordinate increase. The variations in temperature, winds, 

 and birds also have a tendency to prevent their too rapid spread. 



We have alluded to the fact that some species of aphids are subter- 

 ranean, passing their extire existence underground. Among these are 

 the Rhizobiime, which are found on the roots of shrubs and plants, and 

 may be very injurious. These never come to the surface, are wingless, 

 and seem to be cared for by ants, which aid in their distribution. 



